Author: janost

In the menu to the left you’ll find a number of different projects to make with the kit.

101 Synth theory

How do synthesizer make a sound?

A sound is made up of waves of air pressure that your ear drums senses and your brain interprets.

If the rate of the pressure change is above 20 times per second or 20 Hertz your brain interprets it as a tone.

A flute has a chamber like a whistle that make these waves when you blow air through it. A guitar has strings that vibrate to generate the oscillations.

Oscillations is what the sound waves are called and a synthesizer makes them with an oscillator. An electronic device that makes these waves with a voltage.

Our brains can sense a voltage but cant interpret is as a sound but only as a mere tickle if you touch it and it is high enough.

So it needs to be converted to sound waves and that is the job for the speaker. It turns a voltage to a position of a membrane that pushes air and thus turns electric oscillations into sound waves.

These waves can have different shapes. The natural shape is a sine wave. It has no sharp cornes and rises and decend smoothly.

Other waves are the saw wave and square wave. They have a large harmonic content or overtones because of their sharp corners. Harmonics are desired because as you will find out we are going to filter them off to shape the sound.

So we have our sound source. It sounds very boring and monotonic and needs some shaping. That is the job for our next stage, the filter.

The filter is going to gradually remove the overtones we just created. Why create them if we are going to remove them? Because we can do so in a controlled fasion and not static like the oscillator creates them.

The filter attenuates overtones based on the cutoff frequency. A high cutoff lets almost all overtones through while a low cutoff attenuates most of them letting only the fundamental frequency through.

The filter also has some resonance around the cutoff frequency that generates some self oscillation around that point.

Last is the volume part. The amplitude. Some sounds are soft and some are loud.

But it gets better. The oscillator, filter and amp are all controllable. The oscillator can alter its pitch, the filter can alter its cutoff frequency and the amplitude can be changed. With a control voltage.

Control voltages are used to modify the synthesizer in realtime. On the oscillator it controls the pitch, usually from a keyboard. On the filter and amplitude it is controlled from an envelope generator.

The envelope generator is something that generates a voltage in time. Usually controlled by the keyboard gating.

This is what distinguish a piano from strings. On a piano the volume rises instantly when you hit a key and can decay slowly while strings can build up slowly in volume.

And the filter can open instantly and close slowly or open slowly.

The Synth chip

The chip in the makeAsynth kit is the heart of the kit, the synthesizer.

Bat Plus is the battery red wire.
Bat Minus is the battery black wire.
SPK + is the speaker positive wire.
SPK – is the speaker negative wire.
PITCH VC is the control voltage for the oscillator pitch.
FILTER VC is the control voltage for the filter cutoff frequency.
AMP VC is the control voltage for the amplitude level.

A higher voltage to the PITCH VC pin raises the frequency of the oscillator.